The invention concerns a Die Bonder and/or Wire Bonder with a suction device for pulling flat and holding down a curved substrate.
When mounting semiconductor chips on a substrate by means of a so-called Die Bonder, the substrate is transported on a supporting surface in steps of a predetermined distance so that a semiconductor chip can be mounted at the foreseen location. In order that the substrate lies flat on the supporting surface, the supporting surface has a drill hole connectable to a vacuum source for the suction and holding down of the substrate.
Some substrates, for example BGA(copyright)s (Ball Grid Array) which are already equipped with semiconductor chips and which are first to be coated with adhesive and then equipped with a second semiconductor chip or those which are fed to the bonding station of a Wire Bonder for the making of wire connections, can, under certain circumstances, be curved to such an extent that suction of the substrate is unsuccessful.
The object of the invention is to specify a suction device which can hold down even strongly curved substrates level with the supporting surface.
The invention consists in that cavities are foreseen in the supporting surface with raisable and lowerable vacuum grippers made of flexible and in shape stable material. With a Die Bonder, the substrate is always advanced in steps to the dispensing station where adhesive is applied and then to the bonding station where the next semiconductor chip is mounted. With a Wire Bonder, the substrate is always advanced in steps to the bonding station where the wires are attached between the semiconductor chip and the substrate. During the forward feed of the curved substrate the vacuum grippers are lowered into the cavities. As soon as the substrate has reached its position, the vacuum grippers are raised by a predetermined distance by means of a lifting cylinder and vacuum is applied. In this position, the vacuum grippers protrude beyond the level of the supporting surface. As soon as the vacuum gripper touches the underneath of the curved substrate, a more or less well-sealed cavity is created. The pressure difference between the pressure on the upper surface of the substrate (atmospheric pressure) and the pressure in the cavity on the underneath (vacuum) then has the effect that the substrate is pressed flat against the supporting surface whereby the flexible vacuum gripper is compressed. As soon as the processxe2x80x94application of adhesive or mounting of semiconductor chip or wiringxe2x80x94is completed, the vacuum is released and the lifting cylinder is lowered. The solution in accordance with the invention has the advantage that, during forward feed of the substrate, the vacuum grippers are located lowered below the supporting surface and therefore can not interfere with the forward feed of the substrate.
In the following, an embodiment of the invention is described in more detail based on the drawing which is not to scale.